This invention generally relates to a remote monitoring system and, more particularly, to a dynamic callback technique which minimizes the amount of time required to obtain stored information from a plurality of remote units without exceeding the capacity of the telephone network.
U.S. Pat. Nos. 4,241,237 and 4,455,453 to Paraskevakos et al. disclose remote meter reading systems where each of a number of remote units initiate callback at predetermined intervals to a central facility for billing and monitoring purposes. A central complex provides a digital instruction to each remote unit upon the completion of its data transfer. The instruction includes data to control the next scheduled callback time. Such a system cannot, however, be used to dynamically control a callback in response to the incoming rate of calls.
U.S. Pat. No. 4,584,602 to Nakagawa discloses a data collecting system and method which are capable of collecting television audience rating data. A marker signal initiates the callback and, after waiting a predetermined time necessary for other terminal units to transmit their data, each terminal unit automatically dials a predetermined telephone number in order to transmit requested viewing data. Such a system may prove useful where a known number of terminals are calling in, but does not promote an efficient use of phone lines where it is not necessary for each terminal to call in.
U.S. Pat. No. 4,696,029 to Cohen controls the initiation of voting calls through regulation of the visual stimuli which trigger the calls. A control center monitors polling call traffic at a plurality of central offices until it determines that the traffic being generated has reached a level which is not within the traffic-handling capabilities of the central office switching machines. The control center then sends messages which cause character generators at local affiliates to reduce the frequency and/or duration of the visual stimuli until the traffic generated has dropped to a level which is within the traffic handling capabilities of the central office. However, this technique cannot be used where the generation of data cannot be controlled.
In order to appreciate the problem solved by the present invention, it is important to understand at least an overview of the problem of connecting a subscriber by telephone through the telephone network to a cable television headend. By way of example, the subscriber may be assumed to have an ordinary telephone set and be located in a different telephone exchange (central office) area from the telephone exchange serving a private branch exchange located at the cable television headend. In particular, when a subscriber initiates a call, the dial tone serving and switching capacity of the initial telephone exchange, the capacity of trunks connecting the two telephone exchanges, the capacity of the lines serving the private branch exchange, the switching capacity of the private branch exchange, and the busy status of the extensions at the private branch exchange are all factors involved in determining whether two different subscribers associated with a cable television headend are able to achieve a through connection to the headend at the same time. The difficulties in establishing a telephone connection when a large number of remote units are attempting to call the headend are magnified when subscribers, especially those who are located in a small geographic area and would tend to connect to the headend over similar telephone paths, all call in simultaneously.